Cruise control 2 (GR 2)

Applications

The cruise control 2 (GR 2) system is a further development of the autarkic speed control (GR 1).It is used as of E38 and in subsequent series with the exception of cars equipped with electronic engine management (EML) and diesel vehicles with digital diesel electronics (DDE).

The cruise control enables constant driving for speed above 30 km/h irrespective of the type of terrain.Additional functions facilitate convenient speed increase or speed decrease as well as making it possible to drive at a stored speed value.

Functional principle

The cruise control system consists of the operating unit, the control electronics and the electric motor-driven actuator.

The control and operating signals necessary for cruise control are supplied to the control electronics.The throttle position is corrected with the electric motor-driven actuator in order to adjust the driving speed during controlled constant driving to the required set speed value or to change the driving speed during controlled driving.The actuator is controlled by the electronic control system. The feedback of the actuator position to the electronic control system closes the control circuit for positioning the throttle.

When driving is uncontrolled, the throttle is controlled directly by the accelerator pedal.The accelerator pedal always has priority in the throttle open direction (also when cruise control is active).Driving with cruise control is interrupted by a number of different switch-off conditions, e.g. pressing the brake pedal or the clutch pedal.

Note

The cruise control GR 2 is connected directly to a diagnosis link.In the case of faults during the diagnostic procedure, the diagnosis link must be checked between the diagnosis socket and the control unit for cruise control.

Variants

Depending on the vehicle type, vehicle equipment level and country-specific variant, the cruise control is operated either via an operating unit integrated in the steering wheel (multifunction steering wheel, MFL) or with the steering column switch.Operation with the steering column switch can take place with or without the main switch.A further differentiation is made between the type of transmission installed (manual or automatic transmission) and the type of brake light switch (electronic or mechanical).

Variant	Features
1	MFL operating unit, main switch, manual transmission, electronic brake light switch
2	MFL operating unit, main switch, automatic transmission, electronic brake light switch
3	Steering column switch, main switch, manual transmission, electronic brake light switch
4	Steering column switch, main switch, automatic transmission, electronic brake light switch
5	Steering column switch, main switch, manual transmission, electronic brake light switch
6	Steering column switch, main switch, automatic transmission, mechanical brake light switch
7	Steering column switch, manual transmission, mechanical brake light switch
8	Steering column switch, automatic transmission, mechanical brake light switch

Coding

The cruise control (tempomat) control unit is adapted by means of coding data to the various vehicle types, vehicle equipment level and the country-specific function characteristics.

On delivery, the control units already feature basic coding so that the cruise control (tempomat) function is catered for. Slight deterioration with regard to convenient control characteristics can then be expected.Driving situations which endanger safety can arise from incorrect coding of any type whatsoever.

The following information is contained in the coding data:

Description	Values	Remarks
Number of cylinders	4, 6, 8	Number of cylinders of engine
Type of transmission	0 or 1	0 = automatic transmission, 1 = manual transmission
K-number	3433 - 6866	Conversion factor for driving speed
Maximum cruise control (tempomat) speed	30 - 250 km/h	Maximum speed for controlled driving
Type selection	0 - 13	Pointer set to one of 14 tables containing the control data records matching the relevant vehicle type

Cruise control (tempomat) operation

The cruise control (tempomat) GR 2 is operated by means of several operating elements:

Main switch

The main switch is designed as a push button.After switching the ignition lock to position 1 or 2, the cruise control (tempomat) is set ready for operation by pressing the main switch.This standby mode prepares (arms) the system which must be carried out before switching on the cruise control (tempomat). This function is intended to prevent the cruise control (tempomat) being switched on by unintentional operation.

The tempomat standby status is indicated by an LED in the instrument cluster.

After the system has been switched in standby mode and all switch-on conditions have been fulfilled, the cruise control (tempomat) can be set into operation by pressing the "accelerate" button.

Tempomat standby mode is cancelled by pressing the main switch once again.Cruise control (tempomat) operation is then not possible.The cruise control (tempomat) standby can be cancelled at any time irrespective of the relevant vehicle status.The same applies when the ignition lock is switched in position 0 or when the cruise control (tempomat) control unit detects a system defect.

Accelerate

The cruise control (tempomat) is switched on by pressing the "accelerate" button on the steering wheel. When the button is pressed continuously, the speed is additionally increased with a comfortable acceleration progression.

The cruise control (tempomat) is only switched on, however, when all switch-on conditions have been fulfilled.The switch-on conditions are:

Tempomat prepared with main switch (if installed).
Rest position of "accelerate" button before switching on the cruise control (tempomat).
Minimum speed of 30 km/h must be exceeded.
The brake pedal must be in rest position.
On vehicles with manual transmission, the clutch pedal must be in rest position.
On vehicles with automatic transmission, drive stage "2" to "D" must be engaged.
No switch-off conditions must be effective. Switch-off conditions are possible either by operating control elements (e.g. pressing the "OFF" button on the operating unit), or they can arise due to detected defect statuses (e.g. short-circuit at actuator motor).The defects are stored in the form of defect codes in the defect code memory.

After releasing the button, constant driving at the speed currently reached takes effect.

Decelerate

The speed is reduced from controlled cruise control (tempomat) driving by pressing the "decelerate" button on the steering wheel.In this case, the deceleration capacity of the vehicle takes effect. The throttle is moved back from the current status to the idle position.This results in continuous speed reduction provided the braking torque of the engine and the terrain make this possible.

This procedure is effective for as long as the "decelerate" button is depressed.However, it is not possible to drop below the minimum speed.This makes it possible to specifically approach the minimum speed.

After releasing the button, constant driving at the speed currently reached takes effect.

The deceleration procedure can be interrupted by a switch-off condition arising:

Switching off with the main switch
Pressing the brake pedal
Pressing the clutch pedal (manual transmission)
Engaging the drive stages "P" or "N" (automatic)
There must be no defect statuses (e.g. short-circuit at actuator motor).Defects are stored in the form of defect codes in the defect code memory.

Resume

Pressing the "resume" button makes it possible to switch on the cruise control (tempomat) and to automatically approach a speed value already stored with specified acceleration progression and subsequent constant driving speed.A stored speed value can only be approached from uncontrolled driving by pressing the "resume" button.

Tip-up, tip-down

Tip-up:
The driving speed is increased in steps of 1 km/h by briefly hitting the "accelerate" button.
The throttle must be outside the full load position.If this is not the case, button operation is ignored.
Tip-down:
The driving speed is decreased in steps of 1 km/h by briefly hitting the "decelerate" button.

Both functions are only implemented during controlled constant driving.The relevant button must not be pressed for longer than 0.5 s.If the button is pressed longer, the normal function "accelerate" or "decelerate" are carried out.

Comfort cutout

The cruise control is cut out smoothly by pressing the "OFF" button.

On reaching the idle position, however, after 2 s have elapsed at the latest, the positive lock between the throttle and control unit is cancelled by disconnecting the actuator clutch.The actuator remains in this condition until the next time the cruise control (tempomat) is switched on.

Fast cutout

The quick cutout facility cancels the positive lock between the control unit and throttle by opening the actuator clutch.This procedure takes place within 0.5 s.

For safety reasons, the actuator motor is powered in throttle direction until the status "actuator clutch open" is detected.

This cutout condition is triggered by:

Pressing the brake pedal
Pressing the clutch pedal on vehicles with manual transmission
Engaging the drive stages "N" or "P" on vehicles with automatic transmission
Violation of a safety test:The control unit checks the inputs and outputs during cruise control (tempomat) operation.The system is switched off in an implausible condition occurs at the inputs our outputs.

Transmission interface

A connection is provided between the transmission and tempomat control units for automatic vehicles to ensure comfortable driving characteristics for controlled constant driving, acceleration and deceleration procedures.

The requirements of the tempomat control unit necessitates a special transmission program for controlled driving.This transmission program ensures repeated gear change between adjacent gear stages is avoided.

The transmission program takes into consideration following driving statuses:

Driving status	Transmission adaptation
Constant driving	Comfort-oriented, low speed level
Resume	Comfort-oriented, low speed level
Accelerate	Designed to utilise maximum tractive force
Decelerate	Avoids upshifts for optimum deceleration capacity

The information exchange between the tempomat control unit and transmission control unit takes place via a single-wire link from the tempomat control unit to the transmission control unit.Data transfer begins when the control unit supply voltage is applied.The tempomat main switch has no influence on the start and end of data transfer.

If a data transfer fault occurs, for the transmission control this is equivalent to the status "cruise control passive".If, after a data transfer error, correct signals are received once again, they are once again taken into consideration by the transmission control.

Safety checks

The control unit checks the inputs and outputs during cruise control (tempomat) operation.The system is switched off if an implausible status occurs at the inputs or outputs.

Following situations can result in system shut-down:

Minimum speed threshold

The minimum speed threshold (v_min threshold) prevents controlled driving operation below a speed of 30 km/h.

If, before exceeding v_min , a signal was already applied to implement a cruise control (tempomat) function, the cruise control (tempomat) system is not switched on after exceeding this threshold.

All tempomat functions are clear again after cancelling operation in the permissible speed range.

If the speed drops below the v_min threshold from controlled driving operation due to extreme driving situations (e.g. gradient), rapid cutout is implemented.

Implementing a cruise control (tempomat) function

A cruise control (tempomat) function is only carried out if the operating element is in rest position before initiating the function.

The function is implemented with defined significance in order to avoid hazardous situations by simultaneously calling up several cruise control (tempomat) functions.

Significance	Function
High	Brake light switch
	Clutch switch
	Transmission switch
	Tempomat OFF
	Decelerate
	Accelerate
Low	Resume

Overdrive monitor

The actuator clutch is released if the controlled driving speed is exceeded by more than 8 km/h due to excess thrust (driving downhill) or pressing the accelerator pedal. This threshold can be effective under all tempomat conditions.When the clutch is released, the cruise control (tempomat) remains active in the background.The actuator clutch engages once again when the speed drops below the threshold value.

This override cutout facility cancels cruise control when the set speed is exceeded by more than 16 km/h over a period of more than 30 s.

Controlled maximum speed

The permissible controlled maximum speed is limited to a fixed value.This fixed value is defined in the coding data.

Fast cutout is activated if the controlled maximum speed is exceeded by depressing the accelerator pedal.

On reaching the controlled maximum speed by pressing the "accelerate" button, acceleration is ended and the speed is maintained constant.

Deceleration cutout

The cruise control (tempomat) is switched off in the case of excessive vehicle deceleration.In this case, vehicle deceleration is determined with the aid of the speed signal.

For safety reasons, this cutout function is provided in addition to the cutout function via the brake pedal.

Deactivation via drive stage selector lever (automatic)

Fast cutout of the cruise control takes place after the drive stage selector lever is switched during controlled driving out of the drive stage "D" into "N" or "P".

Overrev lockout for manual transmission

Fast deactivation of cruise control takes place in the case of overrevving of the engine speed due to the lack of positive connection between the engine and transmission (e.g. by engaging idle during cruise control without operating the clutch).

The measure for this cutout procedure is a distinct change in engine speed without a corresponding change in driving speed.

Reset time monitoring actuator motor

The reset time of the actuator motor is monitored as soon as a deactivation function has taken place. If the maximum reset time is exceeded, the defect code is stored in the defect code memory and the cruise control (tempomat) cannot be reactivated before the ignition lock is switched off and switched on again.

Maximum reset time for fast cutout:	0.5 s
Maximum reset time for comfort cutout:	2 s

Testing the actuator clutch

After applying the supply voltage, the voltage level at the control unit output to the actuator clutch is permanently monitored. The clutch voltage level is read back and compared with the set status in the control units.

If the two statuses do not agree, the cruise control (tempomat) cannot be switched on or, if switched on, it initiates fast deactivation in conjunction with a defect code being stored in the defect code memory.

Deleting the stored speed value

The stored speed value is deleted when the ignition lock is switched to position 2.

Toggle test

The "toggle test" serves the purpose of monitoring the signal transfer between the operating elements in the multifunction steering wheel (MFL) and the tempomat control unit (GR2).For this purpose, the operating signal contains a regularly changing test bit which is constantly monitored.If no change takes place within 1 second, the fast deactivation function is triggered in conjunction with a defect code being stored in the defect code memory.

Voltage monitoring of the actuator potentiometer

From the time the control unit supply voltage is switched on, the supply voltage of the actuator potentiometer is also monitored.In the case of deviations from the nominal value, cruise control is not permissible or fast deactivation is implemented with a defect code being stored in the defect code memory.

Control monitoring

The control monitoring function is effective after switching on the cruise control (tempomat).In this function, the set position of the throttle is compared with the current position of the throttle by evaluating the actuator potentiometer.

This monitoring facility makes it possible to detect a defect in the actuator or in its actuation.

If the requirements of the test are not fulfilled, the cruise control is switched off and a defect code is stored in the defect code memory.

Control unit-internal tests

A memory test is carried out when the supply voltage is applied.

The correct program run is monitored during operation.

If a defect is found in one of these two tests, the cruise control (tempomat) can no longer be switched on and a defect code is stored in the defect code memory.